The present invention relates to an improved operating mechanism for an electrical switch. More particularly, an operating mechanism is described exhibiting a bi-stable condition which maintains the switch contacts in a closed or opened position until a positive unlatching force is applied to overcome the latching force of the operating mechanism, to permit the switch contacts to be switched from open circuit condition to closed current carrying position or vice versa.
The operating mechanism of the present invention is particularly designed to be used with a low DC voltage, high continuous current electrical shunting switch assembly used for shunting electrochemical cells. In such switch assemblies, the shunting switch preferably has a hermetically sealed body which is evacuated, with high conductivity, cylindrical, reciprocably movable switch contacts sealed through opposed body portions of the switch. Such a shunting switch is set forth in U.S. Pat. No. 4,216,359, and includes an operating mechanism in which a reciprocable mechanical link is connected to one switch contact to effect opening and closing of the switch contacts. In this earlier design, the reciprocable mechanical link included Belleville washer overtravel spring means and a rocking cam link portion which cooperated to latch the switch contacts in the closed contact position, and required a positive unlatching force to be applied to open the switch contacts.
It is highly desirable that the switch contacts be latched or maintained in bi-stable open or closed contact position to prevent accidental switch operation from one contact position to the other. The use of an air or hydraulic cylinder operating mechanism has been proposed for applying the reciprocal force needed to open and close the switch contacts of such electrochemical cell shunting switches. It is desirable to provide as part of such air or hydraulic cylinder operating mechanism a latching means for keeping the contacts open or closed in case of loss of air pressure or hydraulic pressure. It is important to avoid accidental switch closing as well as accidental switch opening because of the potential danger to maintenance personnel working on the cell to which the switch assembly is connected. In typical cell systems, thousands of amperes of low DC voltage continuous current will be flowing either through the cell or the shunt switch. It is thus extremely important that a workman be assured that no accidental current switching takes place while he is working on the non-current carrying portion of the system.
The use of Belleville washers or disc springs as part of vacuum circuit breaker operating mechanisms is seen in U.S. Pat. No. 4,099,039 and U.S. Pat. No. 4,225,763, in which the disc spring is employed to eliminate momentary contact separation or contact bounce upon switch contact closing.